docs: def account(transition, direction=Direction.BIDIRECTIONAL):
      """Return the set of all causal links for a |Transition|.
  
      Args:
          transition (Transition): The transition of interest.
  
      Keyword Args:
          direction (Direction): By default the account contains actual causes
              and actual effects.
      """
      if direction != Direction.BIDIRECTIONAL:
          return directed_account(transition, direction)
  
      return Account(directed_account(transition, Direction.CAUSE) +
                     directed_account(transition, Direction.EFFECT))